tiny fix to code example

Author: gavinking

documentation/src/main/asciidoc/introduction/Advanced.adoc

@@ -658,7 +658,7 @@ List<String> tags;
 ----
 @ElementCollection
 @CollectionTable(name = "author_bios",                 // table name
-        joinColumns = @JoinColumn(name = "book_ssn"))  // column holding foreign key of owner
+        joinColumns = @JoinColumn(name = "book_isbn")) // column holding foreign key of owner
 @Column(name="bio")                                    // column holding map values
 @MapKeyJoinColumn(name="author_ssn")                   // column holding map keys
 Map<Author,String> biographies;

documentation/src/main/asciidoc/introduction/Tuning.adoc

@@ -1041,7 +1041,7 @@ Note that SQL expressions like `lower(title)` must be enclosed in parentheses in
 ====
 It's not clear that information about indexes belongs in annotations of Java code.
 Indexes are usually maintained and modified by a database administrator, ideally by an expert in tuning the performance of one particular RDBMS.
-So it might be better to keep the definition of indexes a SQL DDL script that your DBA can easily read and modify.
+So it might be better to keep the definition of indexes in a SQL DDL script that your DBA can easily read and modify.
 <<automatic-schema-export,Remember>>, we can ask Hibernate to execute a DDL script using the property `javax.persistence.schema-generation.create-script-source`.
 ====